What is the difference between a vent and a drain in steam systems?

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In steam systems, you manage two different things: air/non-condensables and condensate. A vent is used to let air and other non-condensable gases escape from the piping so steam can fill the lines and transfer heat efficiently. If air or similar gases build up, heat transfer drops and system efficiency suffers, and corrosion can occur. Vents are placed at high points and can operate automatically or manually to purge those gases.

A drain, on the other hand, removes condensate—the liquid water formed when steam cools and condenses. Removing this liquid prevents problems like water hammer, keeps steam flow clean, and allows condensate to return to the boiler system. Drains are located at low points or other condensate collection points and can be either manual or automatic depending on the design.

So, the best description is that a vent expels air and non-condensables, while a drain removes condensate.